1. Field of the Invention
The field of this invention relates to ground-level pad mounted transformer installations. The present invention relates to an expanding polymer foam composition containing an insecticide and a method of using the expanding foam as a barrier against insect intrusion.
2. Description of the Related Art
In recent years, the use of underground electrical distribution systems has increased. In the absence of traditional pole lines on which to place transformers, pad mounted transformers have become more common. The pad mounted transformer receives the high voltage underground electrical lines and steps the voltage down to usable household levels.
The above-ground location of the high voltage transformer presents safety concerns. To prevent unintentional contact with the high voltage lines and to prevent vandalism, the ground mounted transformers are encased in a housing. The underground high voltage lines usually enter the housing through a vertical opening in the pad.
The opening in the pad for an underground residential distribution (URD) transformer is normally approximately 30″×12″. The primary and secondary conductors enter the transformer housing through this opening. This opening also provides an unintentional entry into a protected environment for certain pests such as fire ants, snakes and mice.
Fire ants are particularly attracted to the protected areas provided by the transformers. Fire ants are able to enter through a very small opening and can even create passages in the soil beneath the pad which will allow access into the transformer via the underground electrical lines, i.e., the primary and secondary conductors, through the pad opening.
The presence of a fire ant mound within the transformer housing can create a number of problems. For example, the ants may build a mound within the transformer housing by excavating dirt from the cable trench under the pad opening. Subsequent rain causes dirt under the front of the pad to wash into the cable trench. The front end of the pad loses support and begins to tilt. This can cause an internal electrical fault if an energized part is no longer covered by transformer fluid as a result of the shift of the pad from its normal horizontal orientation. A nearby lightning strike can cause a high impulse voltage to surge through the transformer circuits and the high impulse voltage can ground to the transformer housing if, as a result of pad tilting, the energized circuits are not covered and insulated by the transformer fluid.
The tilting can also put stress on conductors, elbows, bushings, bushing inserts and bushing wells which can cause a premature electrical fault caused by mechanical failure such as conductor breakage or disconnection of the conductors and leads. Tilting of the pad can also cause the conductor, which is fixed in place, to bend. This stretches and thins insulation on the outside radius of the conductor reducing the effectiveness of the insulation which may cause a premature fault. The tilting of the pad may also cause transformer fluid to leak from the transformer by damaging bushings connected to the transformer housing.
Since fire ants cannot regulate the temperature and humidity within an ant mound, the fire ants continually move ant larvae and the queen ant to different vertical levels within the ant mound to keep the larvae and queen in an environment having the proper temperature and humidity. Furthermore, the fire ants need to be able to move vertically within the mound in order to access water. Fire ants dig tunnels from the bottom of their mounds down to the water table. Restricting the fire ants' ability to move vertically within an ant mound will cause the ants to die or to move to another location. If a pre-existing barrier exists, which restrict fire ants from being able to move vertically downward within a mound, they are effectively deterred from building a mound at all.
The effectiveness of placing insecticides inside the transformer compartment is limited by EPA regulations requiring insecticide to biodegrade within a relatively short time. It is costly and impractical to renew insecticide treatment of transformer compartments every few months to maintain the presence of active insecticide when a lineman may not need to open the transformer for several years.